In Mohs micrographic surgery, tissue having a tumor, typically a carcinoma on the skin of the head or neck, is excised from a patient under microscopic control. The excised tissue specimen, often called a biopsy, is horizontally sliced to provide tissue sections which are then histologically prepared on slides. The slides are reviewed under a microscope to determine whether the tumor is fully contained in the excised tissue. This is indicated by the absence of the tumor in the edges or margins of the excised tissue. If the tumor is not fully contained in the excised tissue, additional tissue from the patient is excised and the procedure repeated until all tissue sections taken indicate the tumor has been removed from the patient. Mohs surgery permits removal of a tumor with maximum preservation of normal surrounding tissue. Mohs surgery is described in the book entitled MOHS SURGERY FUNDAMENTALS AND TECHNIQUES (Kenneth G. Gross, M. D. et al. eds., 1999).
To prepare each tissue specimen in Mohs surgery, multiple sections or slices are manually made with a microtome, where each section is planar and parallel to each other. Often the tissue specimen is first frozen to make the tissue easier to manipulate and cut by the microtome. However, since numerous sections must be made from each tissue specimen and then histologically prepared on slides, this procedure is both tedious and time consuming.
U.S. Pat. No. 4,752,347 provides a method and apparatus for preparing a tissue specimen for sectioning for Mohs surgery. The patent describes placing an excised tissue specimen on a platform, applying a flexible plastic membrane over the tissue specimen, and evacuating the area between the membrane and the tissue specimen. This retracts the membrane onto the platform and pushes the edges of the tissue specimen into a planar orientation parallel to the platform. While under the pressure of the membrane, the tissue sections may be manipulated by an operator through the membrane until the desired orientation is obtained. The edges of the tissue specimen are thus oriented to flatten the edges of the specimen down. The specimen is then frozen, peeled away from the platform, and sectioned by a microtome. Since the edges of the specimen are oriented planar when sectioned by the microtome, a single section can be made having the edges of interest in Mohs surgery. This procedure is adequate for obtaining a section which can be placed on a slide for review under a microscope, but is not useful with optical imaging techniques, such as provided by confocal microscopes, which can examine a surgically exposed tissue specimen without the need for traditional microtome sectioning or slide preparation.
Confocal microscopes optically section naturally or surgically exposed tissue to produce microscopic images of tissue sections. An example of a confocal microscope is the “VivaScope” manufactured by Lucid Inc. of Henrietta, N.Y. Other examples of confocal microscopes are described in U.S. Pat. No. 5,788,639, published International Patent Application WO 96/21938, and in articles by Milind Rajadhyaksha et al., “In vivo Confocal Scanning Laser Microscopy of Human Skin: Melanin provides strong contrast,” The Journal of Investigative Dermatology, Volume 104, No. 6, June 1995, and Milind Rajadhyaksha and James M. Zavislan, “Confocal laser microscope images tissue in vivo,” Laser Focus World, February 1997, pages 119-127. Further, optically sectioned microscopic images of tissue can be produced by optical coherence tomography or interferometry, such as described in Schmitt et al., “Optical characterization of disease tissues using low-coherence interferometry,” Proc. of SPIE, Volume 1889 (1993), or by a two-photon laser microscope, such as described in U.S. Pat. No. 5,034,613.
One problem with optical imaging of a tissue specimen for Mohs surgery is that the tissue specimen is generally too thick, for example 2-3 mm, to enable optically imaging of the edges of the specimen to determine if the specimen contains all of the tumor. Typically, a confocal microscope is limited to producing adequate images of tissue sections at 100-200 microns. Thus, it would be desirable to optically image a tissue specimen in which the edges of the tissue specimen are oriented planar against an optically transparent surface through which the specimen can be optically sectioned.
In addition, optical imaging systems, such as confocal microscopes, generally require the use of a liquid immersion objective lens directed toward the tissue specimen. This necessitates that the tissue specimen be wetted or immersed in a fluid having an optical index suitable for the objective lens, otherwise, the imaging performance of the system is severely degraded. It is thus also desirable that fluids may be insertable to a properly oriented tissue specimen, and further removable, such that the fluid may be replaced with another fluid to change the imaging characteristics of the tissue.
Although U.S. Pat. No. 4,752,347 describes positioning the edges of a tissue specimen planar on a platform under a plastic membrane held by vacuum to the platform, the tissue specimen described in this patent is mechanically sectioned, rather than optically sectioned. Further, prior to mechanical sectioning, such a specimen is incompatible with optical imaging techniques since fluid cannot be present with a tissue specimen in a vacuum, and the platform does not provide a surface through which optical imaging can be performed. For example, liquids under a vacuum would be suctioned away from the specimen, while gases, under the reduced pressure, would dissolve in any liquids to form bubbles, or such gases may boil or evaporate.
Furthermore, the traditional slides from tissue specimens produced by Mohs surgery must be archived for a minimum retention time in compliance with regulatory requirements, or to enable future reanalysis of the slides for legal purposes. This requires storage of the slides for many years which is cumbersome for large volumes of sectioned tissue specimens. Furthermore, each slide must be labeled in accordance with an identification system to facilitate locating the slides if they are ever needed.
In the area of dialysis, U.S. Pat. No. 5,503,741 describes a device having a sealed vacant chamber formed between two parallel dialysis membranes affixed to each side of a gasket. A needle may be inserted through the gasket to delivery or withdraw a sample from the chamber. The device is used for permitting dialysis, i.e., molecular exchange, between the sample in the chamber and an external solution. Such a device is limited to dialysis and provides no mechanism for retaining a tissue specimen in a planar orientation for optical sectioning.